Ischemic heart disease, or coronary heart disease, kills more Americans per year than any other single cause. In 2004, one in every five deaths in the United States resulted from ischemic heart disease. Indeed, the disease has had a profound impact worldwide. If left untreated, ischemic heart disease can lead to chronic heart failure, which can be defined as a significant decrease in the heart's ability to pump blood. Chronic heart failure is often treated with drug therapy.
Ischemic heart disease is generally characterized by a diminished flow of blood to the myocardium and is also often treated using drug therapy. Although many of the available drugs may be administered systemically, local drug delivery (“LDD”) directly to the heart can result in higher local drug concentrations with fewer systemic side effects, thereby leading to improved therapeutic outcomes.
Cardiac drugs may be delivered locally via catheter passing through the blood vessels to the inside of the heart. However, endoluminal drug delivery has several shortcomings, such as: (1) inconsistent delivery, (2) low efficiency of localization, and (3) relatively rapid washout into the circulation.
To overcome such shortcomings, drugs may be delivered, directly into the pericardial space, which surrounds the external surface of the heart. The pericardial space is a cavity formed between the heart and the relatively stiff pericardial sac that encases the heart. Although the pericardial space is usually quite small because the pericardial sac and the heart are in such close contact, a catheter may be used to inject a drug into the pericardial space for local administration to the myocardial and coronary tissues. Drug delivery methods that supply the agent to the heart via the pericardial space offer several advantages over endoluminal delivery, including: (1) enhanced consistency and (2) prolonged exposure of the drug to the cardiac tissue.
In current practice, drugs are delivered into the pericardial space either by the percutaneous transventricular method or by the transthoracic approach. The percutaneous transventricular method involves the controlled penetration of a catheter through the ventricular myocardium to the pericardial space. The transthoracic approach involves accessing the pericardial space from outside the heart using a sheathed needle with a suction tip to grasp the pericardium, pulling it away from the myocardium to enlarge the pericardial space, and injecting the drug into the space with the needle.
For some patients with chronic heart failure, cardiac resynchronization therapy (“CRT”) can be used in addition to drug therapy to improve heart function. Such patients generally have an abnormality in conduction that causes the right and left ventricles to beat (i.e., begin systole) at slightly different times, which further decreases the heart's already-limited function. CRT helps to correct this problem of dyssynchrony by resynchronizing the ventricles, thereby leading to improved heart function. The therapy involves the use of an implantable device that helps control the pacing of at least one of the ventricles through the placement of electrical leads onto specified areas of the heart. Small electrical signals are then delivered to the heart through the leads, causing the right and left ventricles to beat simultaneously.
Like the local delivery of drugs to the heart, the placement of CRT leads on the heart can be challenging, particularly when the target placement site is the left ventricle. Leads can be placed using a transvenous approach through the coronary sinus, by surgical placement at the epicardium, or by using an endocardial approach. Problems with these methods of lead placement can include placement at an improper location (including inadvertent placement at or near scar tissue, which does not respond to the electrical signals), dissection or perforation of the coronary sinus or cardiac vein during placement, extended fluoroscopic exposure (and the associated radiation risks) during placement, dislodgement of the lead after placement, and long and unpredictable times required for placement (ranging from about 30 minutes to several hours).
Clinically, the only approved non-surgical means for accessing the pericardial space include the subxiphoid and the ultrasound-guided apical and parasternal needle catheter techniques, and each methods involves a transthoracic approach. In the subxiphoid method, a sheathed needle with a suction tip is advanced from a subxiphoid position into the mediastinum under fluoroscopic guidance. The catheter is positioned onto the anterior outer surface of the pericardial sac, and the suction tip is used to grasp the pericardium and pull it away from the heart tissue, thereby creating additional clearance between the pericardial sac and the heart. The additional clearance tends to decrease the likelihood that the myocardium will be inadvertently punctured when the pericardial sac is pierced.
Although this technique works well in the normal heart, there are major limitations in diseased or dilated hearts—the very hearts for which drug delivery and CRT lead placement are most needed. When the heart is enlarged, the pericardial space is significantly smaller and the risk of puncturing the right ventricle or other cardiac structures is increased. Additionally, because the pericardium is a very stiff membrane, the suction on the pericardium provides little deformation of the pericardium and, therefore, very little clearance of the pericardium from the heart.
As referenced above, the heart is surrounded by a “sac” referred to as the pericardium. The space between the surface of the heart and the pericardium can normally only accommodate a small amount of fluid before the development of cardiac tamponade, defined as an emergency condition in which fluid accumulates in the pericardium. Therefore, it is not surprising that cardiac perforation can quickly result in tamponade, which can be lethal. With a gradually accumulating effusion, however, as is often the case in a number of diseases, very large effusions can be accommodated without tamponade. The key factor is that once the total intrapericardial volume has caused the pericardium to reach the noncompliant region of its pressure-volume relation, tamponade rapidly develops. Little W. C. and Freeman G. L. (2006). “Pericardial Disease.” Circulation 113(12): 1622-1632.
Cardiac tamponade occurs when fluid accumulation in the intrapericardial space is sufficient to raise the pressure surrounding the heart to the point where cardiac filling is affected. Ultimately, compression of the heart by a pressurized pericardial effusion results in markedly elevated venous pressures and impaired cardiac output producing shock which, if untreated, it can be rapidly fatal. Id.
The frequency of the different causes of pericardial effusion varies depending in part upon geography and the patient population, Corey G. R. (2007). “Diagnosis and treatment of pericardial effusion.” http://patients.uptodate.com. A higher incidence of pericardial effusion is associated with certain diseases. For example, twenty-one percent of cancer patients have metastases to the pericardium. The most common are lung (37% of malignant effusions), breast (22%), and leukemia/lymphoma (17%). Patients with HIV, with or without AIDS, are found to have increased prevalence, with 41-87% having asymptomatic effusion and 13% having moderate-to-severe effusion, Strimel W. J. et al, (2006). “Pericardial Effusion.” http://www.emedicine.com/med/topic1786.htm.
End-stage renal disease is a major public health problem. In the United States, more than 350,000 patients are being treated with either hemodialysis or continuous ambulatory peritoneal dialysis. Venkat A. et al. (2006). “Care of the end-stage renal disease patient on dialysis in the ED.” Am J Emerg Med 24(7): 847-58. Renal failure is a common cause of pericardial disease, producing large pericardial effusions in up to 20% of patients. Task Force members, Maisch B., Seferovic P, M., Ristic A. D., Erbel R., Rienmuller R., Adler Y., Tomkowski W. Z., Thiene G., Yacoub M. H., ESC Committee for Practice Guidelines, Priori S. G., Alonso Garcia M. A., Blanc J.-J., Budaj A., Cowie M., Dean V., Deckers J., Fernandez Burgos E., Lekakis J., Lindahl B., Mazzotta G., Moraies J., Oto A., Smiseth O. A., Document Reviewers, Acar J., Arbustini E., Becker A. E., Chiaranda G., Hasin Y., Jenni R., Klein W., Lang I., Luscher T. F., Pinto F. J., Shabetai R., Simoons M. L., Soler Soler J., Spodick D. H. (2004). “Guidelines on the Diagnosis and Management of Pericardial Diseases Executive Summary: The Task Force on the Diagnosis and Management of Pericardial Diseases of the European Society of Cardiology.” Eur Heart J 25(7): 587-610.
Viral pericarditis is the most common infection of the pericardium. Inflammatory abnormalities are due to direct viral attack, the immune response (antiviral or anticardiac), or both. Id. Purulent (bacterial) pericarditis in adults is rare, but always fatal if untreated. Mortality rate in treated patients is 40%, mostly due to cardiac tamponade, toxicity, and constriction, It is usually a complication of an infection originating elsewhere in the body, arising by contiguous spread or haematogenous dissemination. Id. Other forms of pericarditis include tuberculous and neoplastic.
The most common secondary malignant tumors are lung cancer, breast cancer, malignant melanoma, lymphomas, and leukemias. Effusions may be small or large with an imminent tamponade. In almost two-thirds of the patients with documented malignancy pericardial effusion is caused by non-malignant diseases, e.g., radiation pericarditis, or opportunistic infections. The analyses of pericardial fluid, pericardial or epicardial biopsy are essential for the confirmation of malignant pericardial disease. Id.
Management of pericardial effusions continues to be a challenge. There is no uniform consensus regarding the best way to treat this difficult clinical entity. Approximately half the patients with pericardial effusions present with symptoms of cardiac tamponade. In these cases, symptoms are relieved by pericardial decompression, irrespective of the underlying cause. Georghiou G. P. et al, (2005). “Video-Assisted Thoracoscopic Pericardial Window for Diagnosis and Management of Pericardial Effusions.” Ann Thorac Surg 80(2): 607-610. Symptomatic pericardiac effusions are common and may result from a variety of causes. When medical treatment has failed to control the effusion or a diagnosis is needed, surgical intervention is required. Id.
The most effective management of pericardial effusions has yet to be identified. The conventional procedure is a surgically placed pericardial window under general anesthesia. This procedure portends significant operative and anesthetic risks because these patients often have multiple comorbidities. Less invasive techniques such as blind needle pericardiocentesis have high complication and recurrence rates. The technique of echocardiographic-guided pericardiocentesis with extended catheter drainage is performed under local anesthetic with intravenous sedation. Creating a pericardiostomy with a catheter in place allows for extended drainage and sclerotherapy. Echocardiographic-guided pericardiocentesis has been shown to be a safe and successful procedure when performed at university-affiliated or academic institutions. However, practices in community hospitals have rarely been studied in detail. Buchanan C. L. et al. (2003). “Pericardiocentesis with extended catheter drainage: an effective therapy.” Ann. Thorac. Surg. 76(3): 817-82.
The treatment of cardiac tamponade is drainage of the pericardial effusion. Medical management is usually ineffective and should be used only while arrangements are made for pericardial drainage. Fluid resuscitation may be of transient benefit if the patient is volume depleted (hypovolemic cardiac tamponade).
Surgical drainage (or pericardiectomy) is excessive for many patients. The best option is pericardiocentesis with the Seldinger technique, leaving a pigtail drainage catheter that should be kept in place until drainage is complete. Sagrista Sauleda J. et al. (2005). “[Diagnosis and management of acute pericardial syndromes],” Rev Esp Cardiol 58(7): 830-41. This less-invasive technique resulted in a short operative time and decreased supply, surgeon, and anesthetic costs. When comparing procedure costs of a pericardial window versus an echo-guided pericardiocentesis with catheter drainage at our institution, there was a cost savings of approximately $1,800/case in favor of catheter drainage. In an era of accelerating medical costs, these savings are of considerable importance. Buchanan C. L. et al., 2003.
Currently, 0.2% of the U.S. population over 45 years of age (nearly 200,000 patients) have reached a stage of severe congestive heart failure (CHF) at which medical therapy is not sufficient to sustain an acceptable level of cardiac function. Since only approximately 2,000 donor hearts are available in the U.S. each year for transplantation, it is necessary to have cardiac support or replacement. Baughman K. L, and Jarcho J. A. (2007). “Bridge to Life—Cardiac Mechanical Support.” N. Engl. J. Med. 357(9): 846-849.
Although there has been important progress in pharmacological treatments for CHF, such as Angiotensin-Converting Enzyme (ACE) inhibitors, beta-blockers, and aldosterone inhibitors that have significantly decreased mortality, the progression from asymptomatic left ventricular dysfunction to symptomatic CHF is still a major issue. Mancini D. and Burkhoff D. (2005). “Mechanical Device-Based Methods of Managing and Treating Heart Failure.” Circulation 112(3): 438-448.
The purpose of many heart failure treatments is to slow, or reverse, the process. Several studies have demonstrated that a pharmacological blockade of the key neurohormonal pathways interrupts the vicious cycle, retards progression, and improves survival. Nevertheless, studies suggest that attempts to block additional neurohormonal pathways may be detrimental. These findings underscore the limit of pharmacological treatments for heart failure. Id.
Regarding devices for treatment of CHF, there have been extensive efforts to develop and test device-based therapies for patients with both acute and chronic heart failure. For example, cardiac resynchronization therapy (CRT), myogenesis (e.g., stem cells and myoblasts) and electrical therapies, such as less invasive defibrillators, are under active investigation. Surgical reshaping of the dilated heart, including a reduction in the radius of curvature, can decrease wall stress, in principle allowing for reverse remodeling. Removal of dyskinetic scar is clinically accepted and reported to be associated with satisfactory outcomes. The effects of removing akinetic scar (often referred to as the Dor procedure or surgical anterior ventricular restoration (SAVR) are also under investigation. Another method proposed to decrease wall stress and to induce reverse remodeling is by passive ventricular restraint devices. This concept evolved from an earlier investigational approach called cardiomyoplasty. Id.
In order to treat symptoms of heart failure due to mitral insufficiency, numerous catheter-based devices are being developed to perform mitral valve repair percutaneously to reduce risk as a non-invasive procedure. Id.
For over 40 years, many researchers have pursued the development of mechanical cardiac support. The earliest forms of clinical use were introduced in 1953 by the cardiopulmonary bypass, and was used for cardiopulmonary support during cardiac surgery. In 1962, the intra-aortic balloon counterpulsation was introduced and used for temporary partial hemodynamic support improving myocardial contractility and coronary perfusion. Neither approach provides full cardiac replacement, however, even temporarily, as each approach is limited by the invasive nature of the procedure, e.g. the requirement for large-bore cannulation of the femoral circulation limits the patient's mobility and restricts functional recovery. Risks of bleeding, thromboembolism, and infection also limit the feasible duration of support. Baughman and Jarcho, 2007.
The intra-aortic balloon pump (IABP) is the most widely used of all circulatory assist devices. Counterpulsation improves left ventricular (LV) performance by enhancing myocardial oxygen balance. It increases myocardial oxygen supply by diastolic augmentation of coronary perfusion and decreases myocardial oxygen requirements through a reduction in the afterload component of cardiac work. Azevedo C. F. et al. (2005). “The effect of intra-aortic balloon counterpulsation on left ventricular functional recovery early after acute myocardial infarction: a randomized experimental magnetic resonance imaging study.” Eur. Heart J, 26(12): 1235-1241.
Support for the use of IABP in patients with acute myocardial infarction (AMI) has been based on the above theoretical consideration. However, the relationship between the beneficial physiological effect of counterpulsation and post-AMI LV functional recovery remains largely undefined. In fact, several studies have investigated the immediate effect of IABP on LV performance and demonstrated that, during counterpulsation, there is a significant improvement in LV haemodynamics.
An important difference exists between the improved haemodynamics provided by counterpulsation itself and the possible favorable effect on post-AMI non-assisted LV contractility. Id. Furthermore, it is important to highlight that at twenty-four hours after reperfusion, the degree of functional recovery was similar with or without IABP counterpulsation. Therefore, even though IABP counterpulsation may have an important role in supporting and improving the clinical status of patients in the early phases of reperfused AMI, it does not seem to have a significant beneficial effect in terms of long-term LV functional improvement. Id.
The available forms of mechanical cardiac support are devices known as pumps that can be classified into three types: centrifugal pumps, volume-displacement pumps, and axial-flow pumps. Moreover, three distinct clinical indications for mechanical cardiac support have been defined. Temporary support is instituted when recovery of native heart function is expected. Among patients who are candidates for heart transplantation but who may not survive the waiting period for a transplant, a ventricular assist device may be used as a “bridge to transplantation.” Ultimately, for patients who are not candidates for heart transplant and for whom recovery of cardiac function is not probable, a mechanical device may be utilized as “destination therapy”; i.e., as a permanent replacement for the native heart. This last indication has only recently been established in clinical practice but is expected to be of growing importance in the future. Baughman and Jarcho, 2007.
Despite the wide variety of pumps currently available, the problems associated with this technology have not changed since the early years of development. Id. Available devices for circulatory support use numerous blood contacting pumps to assist the failing heart. Blood removed from the venous circulation is injected into the arterial circuit in order to increase organ perfusion. Unfortunately, blood contact remains the core for major complications generally associated with mechanical circulatory support. Thromboembolic events, the need for anticoagulation, bleeding, hemolysis, immune suppression, and activation of the inflammatory system are factors which continue to threaten those requiring this therapy. Moreover, device implantation can be difficult and time-consuming which limits feasibility when cardiovascular collapse occurs suddenly. These unsolved problems provide continued motivation to develop non-blood contacting circulatory support devices. Instead of unloading the heart, mechanical forces are directed toward increasing pump performance of the ventricular wall. Anstadt M. P. et al. (2002). “Non-blood contacting biventricular support for severe heart failure.” Ann. Thorac. Surg. 73(2): 556-562. These complex problems may be circumvented by a fundamentally different approach to cardiac assist.
Among all organs, the heart is unique in that oxygen extraction is nearly close to maximal. Thus, the only way that this metabolically demanding organ can increase oxygen consumption is by increasing coronary blood flow. In this aspect of oxygen delivery, the heart is also unique because most flow occurs in diastole instead of in systole. Carabello B. A. (2006). “Understanding Coronary Blood Flow: The Wave of the Future.” Circulation 113(14): 1721-1722.” The compression of the vasculature by the surrounding cardiac muscle during systole impedes flow so that while the pressure head for flow is maximum in systole, flow is maximum in diastole.
Waves are generated from both ends of the coronary vasculature, in that proximal waves move forward and distal waves move backward. In this scheme, proximal “pushing” waves and distal “suction” waves accelerate forward blood flow, while proximal suction waves and distal pushing waves do the converse. Carabello, B. A., 2006. The forward-moving pushing wave is generated by systolic pressure. It drives blood primarily into the epicardial coronaries where it may be stored until it is released for forward flow when the myocardium relaxes. The second important wave, typically the largest, is a suction wave generated by relaxation of the left ventricle and is likely the main driver in diastolic coronary blood flow. Id.
Among patients with ischemic heart disease, it is of great importance to improve the microvascular blood flow in the myocardium to protect the myocardium from infarction. Today, many different drugs and sophisticated techniques, such as percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG), are used with remarkable results. Despite this, there is a large group of patients who have been heavily treated with different drugs (leading to drug-resistant angina pectoris) who have already undergone one or more PCIs or CABG, or both, and who still have serious ischemic heart disease. A satisfactory mode of treatment for these patients has yet to be found. Lindstedt S. et al. (2007). “Blood Flow Changes in Normal and Ischemic Myocardium During Topically Applied Negative Pressure.” Ann. Thorac. Surg. 84(2): 568-573.
Despite the extensive clinical use and excellent outcome of topical negative pressure (TNP) in wound therapy, the fundamental scientific mechanism is, to a large extent, unknown. One of the known effects of TNP is enhanced blood flow to the wound edge, as has been shown in a sternotomy wound model. TNP increases blood flow velocity and opens up the capillary beds. Mechanical forces exerted by TNP and increased blood flow affect the cytoskeleton in the vascular cells and stimulate granulation tissue formation, which involves endothelial proliferation, capillary budding, and angiogenesis. Id.
As described herein, studies have shown that when myocardium was exposed to a topical negative pressure of −50 mm Hg, an immediate significant increase in microvascular blood flow was observed. To investigate whether similar results could be obtained in an ischemic model, the LAD was occluded for 20 minutes. When the ischemic area of the myocardium was exposed to a topical negative pressure of −50 mm Hg, an immediate significant increase in microvascular blood flow was detected. Furthermore, after 20 minutes of reperfusion, myocardial blood flow significantly increased when −50 mm Hg was applied. Lindstedt S. et al, (2007). Similar findings have been made with TNP of −25 mmHg.
TNP stimulation of myocardial blood flow may be a possible therapeutic intervention. It is believed that the sheering forces exerted by TNP stimulate angiogenesis. It has been observed in patients treated with TNP that richly vascularized granulation tissue develops over the heart within 4 to 5 days. These newly formed blood vessels may provide collateral blood supply that is needed when the native circulation fails to provide sufficient blood flow. It may be that the TNP stimulation of blood flow and development of collateral blood vessels in part accounts for the reduced long-term mortality in patients treated with TNP for poststernotomy mediastinitis after CABG. Lindstedt S. et al, (2007).
The pericardium is a conical fibro-serous sac, in which the heart and the roots of the great vessels are contained. The heart is placed behind the sternum and the cartilages of the third to seventh ribs of the left side, in the mediastinal cavity. Gray H. (1918). “Anatomy of the Human Body.” Philadelphia: Lea & Febiger; Bartleby.com, 2000, pp. 1821-1865. The pericardium is separated from the anterior wall of the thorax, in the greater part of its extent, by the lungs and pleurae. However, a small area, somewhat variable in size and usually corresponding with the left half of the lower portion of the body of the sternum and the medial ends of the cartilages of the fourth and fifth ribs of the left side, comes into direct relationship with the chest wall. Behind, the pericardial sac rests upon the bronchi, the esophagus, the descending thoracic aorta, and the posterior part of the mediastinal surface of each lung. Laterally, it is covered by the pleurae, and is in relation with the mediastinal surfaces of the lungs. The phrenic nerve, with its accompanying vessels, descends between the pericardium and pleura on either side. Id.
Similar to synovial joints in which moving surfaces may be separated by a thin fluid film at different stages of stance and walking, the heart and pericardium might be viewed as a load-bearing system in which deformable epicardial and pericardial sliding surfaces are separated by a lubricant. deVries G. et al. (2001). “A novel technique for measurement of pericardial pressure,” Am. J. Physiol. Heart Circ. Physiol. 280(6): H2815-22.
The role played by the pericardium in cardiac hemodynamics is important. Almost a century ago. Barnard concluded that the pericardium can be a significant constraint in filling of the heart. Barnard H. (1898). “The functions of the pericardium.” J. Physiol. 22: 43-47. In a simple experiment, he isolated and inflated the pericardium of a dog with a bicycle pump and observed that it did not rupture until pressures of 950 to 1330 mm Hg. According to Barnard, “when a relaxed heart is subject to a venous pressure of from 10 to 20 mm Hg, the pericardium takes the strain and prevents dilatation of the heart beyond a certain point. Thus the mechanical disadvantages of dilated cavities and of a thinned wall are prevented.” Hamilton D. R. et al. (1994). “Right atrial and right ventricular transmural pressures in dogs and humans. Effects of the pericardium.” Circulation 90(5): 2492-500.
Gibbons Kroeker et al. showed that direct interaction between the left ventricle (LV) and right ventricle (RV) is mediated by the pericardium, as shown by a pericardium-mediated compensation for sudden changes in atrial volume. Gibbons Kroeker et al. (2006), “A 2D FE model of the heart demonstrates the role of the pericardium in ventricular deformation.” Am. J. Physiol. Heart. Circ. Physiol. 291(5): H2229-36. At low strains, the pericardium is extremely distensible, but when strains are greater than ten percent, the pericardium becomes very stiff. Consequently, over a range of lower heart volumes, the pericardium will expand easily with the heart as it fills. At some point, however, it will stiffen and become an ever tighter ring around the minor axis of the heart, resisting further expansion. Id.
Local contact forces between the pericardium and the heart cause regional variation in pericardial deformation during the cardiac cycle, reflecting volume changes of the underlying cardiac chambers. Goto Y. and LeWinter M. M. (1990). “Nonuniform regional deformation of the pericardium during the cardiac cycle in dogs.” Circ. Res. 67(5): 1107-14. The measured left ventricular diastolic pressure is equal to the sum of the pressure differences across the myocardium and the pericardium. Thus, increases in pericardial pressure raise measured ventricular diastolic pressure without change in ventricular volume which causes an upward shift in the pressure-volume curve. Tyberg J. V. et al, (1978). “A mechanism for shifts in the diastolic, left ventricular, pressure-volume curve: the role of the pericardium.” Eur. J. Cardiol. 7 Suppl: 163-75.
Noble gases, also known as the helium family or the neon family, are the elements in group 18 of the periodic table. Noble gases rarely react with other elements since they are already stable. Under normal conditions, they are odorless, colorless, monatomic gases, each having its melting and boiling points close together so that only a small temperature range exists for each noble gas in which it is a liquid. Noble gases have numerous important applications in lighting, welding and space technology. The seven noble gasses are: helium, neon, argon, krypton, xenon, radon, and ununoctium.
Helium (He) is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2. The boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions. Helium is less water soluble than any other gas known, and it does not have any measurable viscosity because the speed of sound in helium is nearly three times the speed of sound in air.
Neutral helium at standard conditions is non-toxic, plays no biological role, and is found in trace amounts in human blood. The addition of helium to a gas mixture prevents the occurrence of ventricular fibrillation. Helium has a definite protective effect against ventricular fibrillation when this preparation is used. The mechanism of the protective effect remains to be established. It is believed that helium may increase collateral circulation in the ischemic area. Pifarre R. et al. (1969). “Helium in the Prevention of Ventricular Fibrillation.” Chest 56(2): 135-138.
Clearly, there is a clinical need for a safe and effective approach to treat patients with congestive heart failure.